循环try / catch语句

Question

I'm trying to take two random rowid from my database. Everything works but I have a scenario when there is only one rowid. I want to make a loop on my try/catch until there is second number in my database.
What I'm doing wrong? Thank you

public void Kaslaimejo() {
    String sql = "SELECT rowid FROM Zaidejai WHERE Pirmas < 4 ORDER BY random() LIMIT 2";
    Integer value1 = null, value2 = null; 
    Integer judesiukas1 = null, judesiukas2 = null;

    int a = 0;
    int k = 15; // kiek kartu? Reikia infinity padaryti

    for (a = 0; a < 3; a++) {
        try {
            Connection conn = Serveris.connect();
            Statement stmt  = conn.createStatement();
            ResultSet rs = stmt.executeQuery(sql)) {
                if (rs.next()) {
                    value1 = rs.getInt("rowid");
                    if (rs.next()) {
                        value2 = rs.getInt("rowid");
                        PreparedStatement buvo = conn.prepareStatement("UPDATE Zaidejai SET Numeriukas = ? WHERE rowid = ?");
                        buvo.setInt(1, i);
                        buvo.setInt(2, value1);
                        int buvolala = buvo.executeUpdate  ();
                        PreparedStatement buvo2 = conn.prepareStatement("UPDATE Zaidejai SET Numeriukas = ? WHERE rowid = ?");
                        buvo2.setInt(1, i);
                        buvo2.setInt(2, value2);
                        int buvolala2 = buvo2.executeUpdate  ();// 
                        i++;
                    }
                System.out.println("Pirmas zaidejas" + value1); // atspausdina 1 random zaideja is duomenu bazes
                System.out.println("Antras zaidejas" + value2); // atspausdina 2 random zaideja is duomenu bazes
            }
        } catch (SQLException e) {
            a--;
            //System.out.println(e.getMessage());
        }
    }
}

Right now my program loops two times and then gives me SQLException . How I can loop my program until there is no SQLException ?

Answer 1

How i can loop my program until there is no SQLException?

Change this (because, it will only allow to loop two times)

for (a = 0; a < 2; a++) {

to

while(true)

Put everything inside while(true) , if exception occurred, then it will come out from the while loop. Something similar :

try
{
  while(true)
  {
  ...
  ...
  }
  ...
}
catch(SQLException e)
{
    // do somthing
}

Answer 2

The logic becomes easier if you add the values to a list

var values = new ArrayList<Integer>();
while (values.Count < 2) {
    try (Connection conn = Serveris.connect();
         Statement stmt  = conn.createStatement();
         ResultSet rs = stmt.executeQuery(sql))
    {
        while (values.Count < 2 && rs.next()) {
            Integer v = rs.getInt("rowid");
            values.Add(v);
        }
    } catch (SQLException e) {
    }
}
//TODO: process the values here

The advantage is, that you can retrieve one value at the first database query and the second at a later one or both in the same round and you don't have to keep track of which one of two variables to use.

(Bear with me with the syntax details, I'm not a Java programmer.)

Answer 3

OK, I've tried to write what I think you're trying to do. You wait for ever until someone puts at least two entries in the database. You extract two values, process them, then wait some more.

Some points to watch out: 1. Object comparisons need to be made with .equals() not with == 2. You might want to provide some way to break out of the infinite loop I've written ( while(true) ). 3. Careful with null values. They might produce NullPointerException . 4. Try to break up your code into methods. Each large block of code could go into each own method.

public void Kaslaimejo(){
    String sql = "SELECT rowid FROM Zaidejai WHERE Pirmas < 4 ORDER BY random() LIMIT 2";
    Integer judesiukas1 = null, judesiukas2 = null;


    while(true) {

        List<Integer> values = new ArrayList<>();

        while (values.size() < 2) {
            try (Connection conn = Serveris.connect();
                 Statement stmt = conn.createStatement();
                 ResultSet rs = stmt.executeQuery(sql)) {
                if( rs.next() ){
                    Integer value = rs.getInt("rowid");
                    values.add(value);
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        try( Connection conn = Serveris.connect()) {
            PreparedStatement buvo = conn.prepareStatement("UPDATE Zaidejai SET Numeriukas = ? WHERE rowid = ?");
            buvo.setInt(1, i);
            buvo.setInt(2, values.get(0));
            int buvolala = buvo.executeUpdate  ();
            PreparedStatement buvo2 = conn.prepareStatement("UPDATE Zaidejai SET Numeriukas = ? WHERE rowid = ?");
            buvo2.setInt(1, i);
            buvo2.setInt(2, values.get(1));
            int buvolala2 = buvo2.executeUpdate  ();//
            i++;
        }catch (SQLException e) {
            e.printStackTrace();
        }

        Connection conn = Serveris.connect();

        try {
            PreparedStatement pstmt = conn.prepareStatement("SELECT Pirmas FROM Zaidejai WHERE rowid = ?");
            PreparedStatement pstmt2 = conn.prepareStatement("SELECT Pirmas FROM Zaidejai WHERE rowid = ?");
            pstmt.setInt(1, values.get(0));
            pstmt2.setInt(1, values.get(1));
            ResultSet myrsv = pstmt.executeQuery();
            ResultSet myrsv2 = pstmt2.executeQuery();


            {

                if (myrsv.next()) {
                    judesiukas1 = myrsv.getInt("Pirmas");
                    if (myrsv2.next()) {
                        judesiukas2 = myrsv2.getInt("Pirmas");
                    }

                }
                //System.out.println("Pirmo zaidejo veiksmas" + myrsv.getInt("Pirmas"));
                //System.out.println("Antro zaidejo veiksmas" + myrsv2.getInt("Pirmas"));

            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }

        if (judesiukas1.equals(judesiukas2)) // careful here. NullPointerException may happen.
        {
            try {
                PreparedStatement laim = conn.prepareStatement("UPDATE Zaidejai SET Rezultatas = ? WHERE rowid = ?"); // ble ble update reikia naudoti , o ne insert into. Insert kai sukuriame nauja kazka tik
                PreparedStatement laim2 = conn.prepareStatement("UPDATE Zaidejai SET Rezultatas = ? WHERE rowid = ?");
                laim.setString(1, "Lygiosios");
                laim.setInt(2, values.get(0));
                laim2.setString(1, "Lygiosios");
                laim2.setInt(2, values.get(1));
                int irasyk = laim.executeUpdate  (); // kodel executeupdate, o ne executequery????
                int irasyk2 = laim2.executeUpdate  (); // kodel executeupdate, o ne executequery????
                {


                }
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.print("Lygiosios");
        } else {

            //  (1) - Rock
            //  (2)  Scissors
            //  (3) - Paper
            switch (values.get(0)){
                case 1:
                    if (judesiukas2 == 2)
                        System.out.print("Zaidejas 1 wins!");

                    else
                        System.out.print("Zaidejas 2 wins!");
                    break;
                case 2:
                    if (judesiukas2 == 3)
                        System.out.print("Zaidejas 1 wins!");
                    else
                        System.out.print("Zaidejas 2 wins!");
                    break;
                case 3:
                    if (judesiukas2 == 1)
                        System.out.print("Zaidejas 1 wins!");
                    else
                        System.out.print("Zaidejas 2 wins!");
                    break;
            }
        }

        try {
            conn.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}